HTML Guide for XML 1.0

XML 1.0 names, typically used for the id attribute of elements, must comply with specific constraints, such as:

• Must start with a letter or underscore _
• Subsequent characters can be letters, digits, hyphens -, underscores _, and periods .
• Cannot contain any spaces or special characters

Here’s an example of an invalid name for an ID:

<svg>
  <g id="Group 270">
    <!-- Content inside the group element -->
  </g>
</svg>

This can be fixed by avoiding whitespace inside the name, like this:

<svg>
  <g id="group-270">
    <!-- Content inside the group element -->
  </g>
</svg>

In this example, the id attribute value Group 270 has been changed to group-270 to follow the rules for XML 1.0 names.

Malformed comment syntax has been found, check out the affected comment.

HTML comments are helpful to leave notes about the code right next to it. To create a comment, it must start with <!-- and end with -->, as in this example:

<!-- Good comment -->

<!--
Comments can
be multi-line
-->

A common cause for a malformed comment is using too many hyphens (-) as in this example:

<!-- Wrong comment -->